1. Field of the Invention
The present invention relates to a voltage conversion device, and more particularly to a voltage conversion device provided with a function of controlling a duty ratio by switching using a semiconductor element. Further, the present invention relates to an application to an electric car.
2. Description of the Related Art
A voltage conversion device is an electric power conversion device which converts an input voltage from a direct-current power source into a desired output voltage. Based on switching using a semiconductor element, stepping up or down of a voltage can be performed by changing a ratio of a consumption time of an input voltage and a consumption time of an output voltage. For example, in an electric car, an output voltage boosted by a direct-current chopper as a voltage conversion device is converted into an alternating current by an inverter, thereby driving an alternating-current motor.
Japanese Patent Application Laid-open No. 308935-1990 discloses a configuration which determines a breakdown in a step-up/down chopper circuit based on a failure of a boosted voltage. Further, Japanese Patent Application Laid-open No. Hei 2-260610 discloses a configuration which boosts a power supply voltage by duty control of a step-up chopper and converts the boosted voltage into an alternating current in an inverter so that a motor is operated with the converted current. Furthermore, Japanese Patent Application Laid-open No. 2001-275367 discloses a configuration which provides a limiter for a current command to avoid an excess current in a structure which performs PI control in a step-up chopper device to obtain the current command.
It is desirable that a voltage conversion device, which often forms a basic structure in an electric system, is capable of rapidly detecting any generated failure. However, a configuration in which a sensor or the like for detecting a failure is formed as a dual system has an inconvenience in terms of a cost. Moreover, in an electric car or the like, even if some of components fail to operate properly, the failed parts must be specified in detail in order to for traveling to continue.
The present invention advantageously provides a failure judging mechanism having a simple configuration.
Additionally, the present invention advantageously enables multi-level setting of a failure judgment criterion in accordance with an operating status of an apparatus.